A programmable display device is an operational display device having an interface with a host controller (PLC), and having functions such as for displaying an operating condition of a device connected to the host controller and receiving from a screen an operational input for providing control instructions to the device. Generally, a programmable display device has a graphical display function, and accordingly can display a console, a switch, a display lamp and the like, so as to serve as an operating terminal in a controlling system.
A screen displayed on such a programmable display device can be created by a user, using screen creation software, according to a specification of a controlling system. In creating a screen, the user uses parts, a drawing function and the like provided by the screen creation software in a personal computer and the like, so as to create a desired screen.
The parts are images for illustrating a switch, a numeric keypad, a meter display device, a graph display device and the like, and are provided in a library form in the screen creation software so as to be combined and used in the same manner as real parts. Further, the parts are used in a manner where images for showing the parts, and assigning data for displaying dynamic changes of the images on a specified position of the screen, are combined with one another. The assigning data is stored as a portion of screen data in a memory of the programmable display device.
The created screen is transferred as the screen data to the programmable display device and stored therein. When the host controller is in operation, an output part such as the meter display device, displayed on the screen displayed on a display section of the programmable display device, changes dynamically according to a condition of a device connected to the host controller. Further, input operations performed on the screen at an input part displayed on the screen, such as a switch, is provided to the device as control instructions.
Further, the created screen is managed in such a manner that it is able to be called back by a screen number, and is managed as a series of related plural screens with respect to a target system that is an object of controlling. For example, Japanese Laid-Open Patent Publication No. 105147/1998 (Tokukaihei 10-105147) (published date; Apr. 24, 1998) discloses a technique in which a project file is constituted of one or more unit screen files and each screen is managed.
It has been general so far that a single programmable display device stores a single project file. In such a case, for example, as for a programmable display device that can be connected with two PLCs, screens corresponding to each PLC are created in one project file, and a screen corresponding to a selected PLC is called back. In a screen displaying a switch for switching PLCs, the switch is operated, and thereby PLCs are switched (a PLC is selected).
However, in recent limited production of a wide variety of products, in order to deal with a wide variety of products by a single production line, it is necessary for a single project file to include screens corresponding to production lines of all kinds of products. As a result, multiple screens are included in a single project file, resulting in such an inconvenience that a management of screens in the project file becomes complex, and a memory capacity for storing the project file in the programmable display device is used up.
In order to avoid a shortage of the memory capacity, there is known the following method. In this method, with respect to each switching of production lines, the project file in use which is stored in the memory of the programmable display device is backed up in a storage medium, and on the other hand a project file corresponding to a production line to be switched, which project file is separately backed up in the storage medium, is transferred to the programmable display device. However, in such a method, it takes much time to transfer the project file, and therefore it is impossible to promptly change production lines according to frequent changes of products.